1. Field of the Invention
Aspects of the present embodiments relate to a laser irradiation apparatus, an irradiation method using the same, and a method of crystallizing an amorphous silicon film. Some embodiments relate to a laser irradiation apparatus which can reduce deviation of the intensity of a laser beam, an irradiation method using the same, and a method of crystallizing an amorphous silicon film which can improve uniformity in crystallization into a polycrystalline silicon thin film.
2. Description of the Related Art
Flat panel display devices such as an organic light emitting diode (OLED) display device or TFT-LCD devices have been widely studied because they can be fabricated in a very thin and flexible structure due to driving characteristics.
Among these flat panel display devices, an active matrix flat panel display device has a pixel circuit disposed in each pixel, and the pixel circuit adjusts and drives an emitting element of each pixel in response to signals applied from a scan line and a data line.
Each pixel circuit includes a thin film transistor, which includes an active layer having a channel. The active layer is generally formed of amorphous silicon or polycrystalline silicon.
While the thin film transistor using the amorphous silicon can be deposited at low temperature, it cannot be used for a large-sized display device. For this reason, polycrystalline silicon has been widely used to fabricate thin film transistors. Polycrystalline silicon is suitable for a large-sized flat panel display device due to high mobility, a high-frequency operating characteristic and a low leakage current.
Such polycrystalline silicon is formed by crystallizing amorphous silicon by a predetermined crystallization method, which is usually laser crystallization.
A laser annealing process of forming an active layer, e.g., a poly-silicon layer, on a substrate is performed by irradiating a linear laser beam having a predetermined length and width to an entire surface of the substrate. The linear laser beam is scanned over the substrate and overlaps to irradiate.
Usually, a pulse laser beam of an excimer laser is used as the laser beam for laser annealing.
The oscillated laser beam is not uniform in every case, which may be caused by a change in temperature due to heating of a laser oscillator, and changes in temperature and deflection of a condenser lens of an optical system.
The non-uniformity of the laser beam results in non-uniform crystallization, which results in a non-uniform resistance generated during fabrication of a thin film transistor. Thus, the non-uniform crystallization can be a direct cause of product defects.